1. Field of the Invention
The present invention relates to an engine in which a sprocket is fixed to one end of a camshaft supported in a cylinder head via a camshaft holder and a timing chain is wrapped around the sprocket and, in particular, to a timing chain lubricating structure therefor.
2. Description of the Related Art
A camshaft of an overhead camshaft type engine is driven by an arrangement in which a sprocket fixed to a shaft end of the camshaft is linked to a sprocket fixed to a shaft end of a crankshaft via a timing chain. A lubricating structure for such a timing chain is known in Japanese Patent Application Laid-open No. 6-146838. The timing chain lubrication structure disclosed in the above-mentioned application has an arrangement in which a relief valve is provided in an oil passage for supplying oil to a hydraulic tappet, and the section where the sprocket is meshed with the chain is lubricated with a jet of oil that issues from an oil jet that is integral with the relief valve.
The above-mentioned conventional arrangement has a problem in that an oil jet is required thus increasing the number of parts, which is a main factor for an increase in the cost, and because the oil jet is formed integrally with the relief valve if the oil jet is placed in a position that is suitable for lubricating the section where the sprocket is meshed with the chain the degree of freedom with which the relief valve can be mounted would be limited.
The present invention has been carried out in view of the above-mentioned circumstances, and it is an object of the present invention to enable the section where a camshaft sprocket is meshed with a timing chain to be reliably lubricated by a simple structure.
In order to achieve the above-mentioned object, in accordance with a first aspect of the present invention, there is proposed a timing chain lubricating structure for an engine in which a sprocket is fixed to an end of a camshaft supported in a cylinder head via a camshaft holder and a timing chain is wrapped around the sprocket wherein a relief oil passage is formed in the plane of a joined surface of the camshaft holder, and an oil drain hole provided at the downstream end of the relief oil passage opens so as to face the section where the sprocket is meshed with the timing chain or the timing chain prior to the meshed section.
In accordance with the above-mentioned arrangement, because the sprocket and the timing chain are lubricated with oil that flows out of the oil drain hole provided at the downstream end of the relief oil passage, it becomes unnecessary to employ an oil jet, thus reducing the number of parts. Moreover, because the relief oil passage is formed in the plane of the joined surface of the camshaft holder, the relief oil passage can easily be formed.
Furthermore, in accordance with a second aspect of the present invention, in addition to the above-mentioned first aspect, there is proposed a timing chain lubricating structure for an engine wherein a hydraulic control valve for discharging oil to the relief oil passage is mounted on a cylinder head side wall that is close to the oil drain hole.
In accordance with the above-mentioned arrangement, because the hydraulic control valve for discharging oil to the relief oil passage is mounted on the side wall of the cylinder head, not only can the rigidity with which the hydraulic control valve is mounted be enhanced, but also the length of the relief oil passage can be reduced because the hydraulic control valve is mounted in a position close to the oil drain hole.
Furthermore, in accordance with a third aspect or a ninth aspect of the present invention, in addition to either the above-mentioned first aspect or second aspect, there is proposed a timing chain lubricating structure for an engine wherein a timing chain is wrapped around sprockets that are fixed to ends of an intake camshaft and an exhaust camshaft respectively, a chain guide for guiding the timing chain is fixed to cam caps of the two camshafts, the cam cap of the intake camshaft and the cam cap of the exhaust camshaft is linked integrally to each other via a connecting wall so as to form a camshaft holder, and a recess is formed in the face of the connecting wall opposite the chain guide.
In accordance with the above-mentioned arrangement, because the cam cap of the intake camshaft and the cam cap of the exhaust camshaft are linked integrally to each other via the connecting wall so as to form the camshaft holder and the chain guide is fixed so as to bridge the recess formed between the two cam caps and the connecting wall, the rigidity can be enhanced by connecting the two cam caps via the connecting wall and the chain guide while reducing the weight of the camshaft holder by means of the recess, and the rigidity with which the intake camshaft and the exhaust camshaft are supported can thus be enhanced.
Furthermore in accordance with a fourth aspect of the present invention, in addition to the above mentioned third aspect, there is proposed a timing chain lubricating structure for an engine wherein the camshaft holder is fastened to the cylinder head by means of outer bolts placed outside the intake camshaft and the exhaust camshaft, the camshaft holder and the chain guide are together fastened to the cylinder head by means of inner bolts placed inside the intake camshaft and the exhaust camshaft, and the seats of the outer bolts are formed so as to be lower than the seats of the inner bolts.
In accordance with the above-mentioned arrangement, because the camshaft holder and the chain guide are together fastened to the cylinder head by means of the common inner bolts, the number of bolts can be reduced. Moreover, because the seats of the outer bolts placed outside the two camshafts are formed so as to be lower than the seats of the inner bolts placed inside the two camshafts, the dimensions of the camshaft holder can be reduced and the dimensions of the engine can be reduced accordingly.
Furthermore, in accordance with a fifth aspect or a sixth aspect of the present invention, in addition to the above-mentioned third aspect or fourth aspect, there is proposed a timing chain lubricating structure for an engine wherein a tooth skipping prevention plate is formed integrally with the chain guide.
In accordance with the above-mentioned arrangement, because the tooth skipping prevention plate if formed integrally with the chain guide, the rigidity of the chain guide can be enhanced by the presence of the tooth skipping prevention plate.
Furthermore, in accordance with a seventh aspect or an eighth aspect of the present invention, in addition to the above-mentioned third aspect or fourth aspect, there is proposed a timing chain lubricating structure for an engine wherein the chain guide has a sliding member made of a resin, the sliding member being in sliding contact with the timing chain.
In accordance with the above-mentioned arrangement, because the resin-made sliding member in sliding contact with the timing chain is provided on the chain guide, not only can wear of the timing chain be suppressed, but also the sliding resistance between the chain guide and the timing chain can be reduced.
Furthermore, in accordance with a tenth aspect of the present invention, in addition to the above-mentioned first aspect, there is proposed a timing chain lubricating structure for an engine wherein the camshaft holder comprises an upper camshaft holder and a lower camshaft holder and the oil drain hole is formed in the lower camshaft holder close to the meshed section.
In accordance with the above-mentioned arrangement, because the camshaft holder comprises the upper camshaft holder and the lower camshaft holder and the oil drain hole if formed in the lower camshaft holder close to the meshed section, it is possible to prevent the oil passage from becoming complicated.
Furthermore, in accordance with an eleventh aspect of the present invention, in addition to the above-mentioned tenth aspect, there is proposed a timing chain lubricating structure for an engine wherein a rocker arm shaft provided beneath the camshaft is supported in the lower camshaft holder and the oil drain hole is provided in the plane in which the lower camshaft holder and the cylinder head are joined together.
In accordance with the above-mentioned arrangement, because the rocker arm shaft provided beneath the camshaft is supported in the lower camshaft holder and the oil drain hole is provided in the plane in which the lower camshaft holder and the cylinder head are joined together, the oil drain hole can be formed by making use of a thick part of the lower camshaft holder that functions as a rocker arm shaft holder.
Furthermore, in accordance with a twelfth aspect of the present invention, in addition to the above-mentioned eleventh aspect, there is proposed a timing chain lubricating structure for an engine wherein the oil drain hole and the rocker arm shaft are provided on either side of the camshaft so that the camshaft is interposed therebetween.
In accordance with the above-mentioned arrangement, because the oil drain hole and the rocker arm shaft are provided on either side of the camshaft so that the camshaft is interposed therebetween, the oil drain hole is provided effectively using a space opposite to the rocker arm shaft thus preventing any increase in the dimensions of the lower camshaft holder.
Furthermore, in accordance with a thirteenth aspect or a fourteenth aspect of the present invention, in addition to either the above-mentioned second aspect or twelfth aspect, there is proposed a timing chain lubricating structure for an engine wherein the oil drain hole is provided closer to the hydraulic control valve than to the axis of the camshaft that is placed on the hydraulic control valve side.
In accordance with the above-mentioned arrangement, because the oil drain hole is provided closer to the hydraulic control valve than to the axis of the camshaft that is placed on the hydraulic control valve side, the length of the oil passage can be further reduced.
Furthermore, in accordance with a fifteenth aspect of the present invention, in addition to the above-mentioned first aspect, there is proposed a timing chain lubricating structure for an engine wherein the relief oil passage is provided along a camshaft holder fastening bolt for fastening the camshaft holder.
In accordance with the above-mentioned arrangement, because the relief oil passage is provided along the camshaft holder fastening bolt for fastening the camshaft holder, leakage of oil from the joined surfaces can be prevented.
Furthermore, in accordance with a sixteenth aspect of the present invention, in addition to the above-mentioned first aspect, there is proposed a timing chain lubricating structure for an engine wherein the camshaft holder is fastened by camshaft holder fastening bolts provided on either side of the camshaft axis and one of the camshaft holder fastening bolts that is closer to the relief oil passage is shorter than the other camshaft holder fastening bolt.
In accordance with the above-mentioned arrangement, because the camshaft holder is fastened by the camshaft holder fastening bolts provided on either side of the camshaft axis and the one of the camshaft holder fastening bolts that is closer to the relief oil passage is shorter than the other camshaft holder fastening bolt, the force with which the camshaft holder is fastened can be increased thus suppressing leakage of oil from the joined surfaces.
Furthermore, in accordance with a seventeenth aspect of the present invention, in addition to the above-mentioned fourth aspect, there is proposed a timing chain lubricating structure for an engine wherein the relief oil passage is provided closer to an outer bolt than to an inner bolt.
In accordance with the above-mentioned arrangement, because the relief oil passage is provided closer to the outer bolt than to the inner bolt, the force with which the camshaft holder is fastened can be increased thus suppressing leakage of oil from the joined surfaces.
Furthermore, in accordance with an eighteenth aspect of the present invention, in addition to the above-mentioned first aspect, there is proposed a timing chain lubricating structure for an engine wherein the relief oil passage is provided between a camshaft holder fastening bolt for fastening the camshaft holder and the sprocket.
In accordance with the above-mentioned arrangement, because the relief oil passage is provided between the camshaft holder fastening bolt for fastening the camshaft holder and the sprocket, the oil drain hole can be made closer to the section that is to be lubricated thus enhancing the lubrication efficiency.
Furthermore, in accordance with a nineteenth aspect of the present invention, in addition to the above-mentioned eighteenth aspect, there is proposed a timing chain lubricating structure for an engine wherein the relief oil passage is provided along the camshaft holder fastening bolt.
In accordance with the above-mentioned arrangement, because the relief oil passage if provided along the camshaft holder fastening bolt, it is possible to suppress leakage of oil from the joined surface of the camshaft holder.
Furthermore, in accordance with a twentieth aspect of the present invention, in addition to the above-mentioned first aspect, there is proposed a timing chain lubricating structure for an engine wherein the oil drain hole is provided on the side of the sprocket that is close to a hydraulic control valve that discharges oil to the relief oil passage.
In accordance with the above-mentioned arrangement, because the oil drain hole is provided on the side of the sprocket that is close to the hydraulic control valve that discharges oil to the relief oil passage, the oil passage can be shortened.
An exhaust camshaft 13 of the embodiments corresponds to the camshaft of the present invention, an intake camshaft sprocket 15 and an exhaust camshaft sprocket 16 of the embodiments correspond to the sprockets of the present invention, a lower camshaft holder 25 of the embodiments corresponds to the camshaft holder of the present invention, bolts 28 and 29 of the embodiments correspond to the inner bolts of the present invention, bolts 27 and 30 of the embodiments correspond to the outer bolts of the present invention, a first hydraulic control value 34 of the embodiments corresponds to the hydraulic control value of the present invention, and an oil passage P7 of the embodiments corresponds to the relief oil passage of the present invention.